The Boring Company has raised a new round of funding worth $675 million, with Elon Musk’s grand plan to “solve traffic” with tunnels now valued at $5.675 billion.

In a blog post announcing the news, the company reiterated its goals and achievements so far, drawing particular attention to its “next generation” of Prufrock tunnel-boring machines (TBMs).

“Unlike traditional TBMs which require upwards of a dozen or more people to operate, Prufrock is designed to be capable of operating completely remotely and autonomously via computerized systems and requires zero people in the tunnel to operate,” said the company. “The current iteration of Prufrock, called Prufrock-2, is designed to mine at up to 1 mile/week, meaning a tunnel the length of the Las Vegas strip (approximately 4 miles) can be completed in a month.”

So far, The Boring Company has built just two operational 0.8-mile tunnels underneath the Las Vegas Convention Center, as well as 1.1-mile test tunnel in Hawthorne, California. The company has been pitching its services far and wide, and although many projects have run aground, authorities in Las Vegas last year approved the construction of a 29-mile tunnel system containing 51 stations.

Image: The Boring Company

The Boring Company describes its tunnels as a “public transportation system that resembles an underground highway” but — more succinctly and accurately — as “Teslas in tunnels.” Originally, Musk said the company’s tunnels would use autonomous sleds to carry cars and specially-designed pods at speeds of up 150mph to transport pedestrians and cyclists. So far, they’re currently limited to electric vehicles (Teslas) driven by human employees at around 50mph and carrying ticketed passengers.

The company’s Las Vegas tunnels have been open for a few years now, and first-hand impressions have been mixed to say the least. When everything goes to plan, the company’s tunnels let cars pass through them at sedate speeds. But when they’re busy they also create their own traffic jams — the very problem they’re intended to solve.

Investors, though, don’t necessarily care whether or not founders like Musk ultimately follow through on their hyperbole, only that the companies they run attract enough customers and revenue to pay back their own investments. And Musk has proved, time and time again, that’s he’s very good at pushing up share prices and valuations. For the meantime, that means The Boring Company has a lot of tunnels left to dig.